This invention relates to a system for controlling the movement of a body, such as an elevator car, between a point a fixed distance from a landing and the landing itself. It will be understood that although the invention is described as applied to a landing computer for an elevator system, it may also be applied to other systems.
Numerous systems are presently known for controlling the movement of an elevator car. Typically, they include an electronic drive circuit for generating a speed pattern which controls the movement of the car in a run mode. The electronic drive circuit receives such information as elevator car position, calls registered, and distance to the next called landing, and produces a speed pattern which accelerates the car to a maximum allowable speed for the distance to be traveled, maintains that speed if sufficient distance remains to the next selected landing, and decelerates the car toward the selected landing. Feedback control of the running speed pattern may be based on car velocity information or absolute position information relative to the desired velocity or instantaneous position. The drive circuit speed pattern is generally a variable voltage, which is applied to the drive motor of the elevator system. The elevator car may run at a maximum speed of from two hundred to five hundred feet per minute in a moderate speed elevator, and up to eighteen hundred feet per minute or more in a high speed elevator.
Regardless of the type of run mode circuitry utilized in an elevator system, a separate landing circuit is generally provided to bring the car to a level stop at the selected landing.
The separate landing circuit generally takes control of the elevator car at the leveling zone, which may extend from about ten to thirty inches from the landing. The landing circuit is required because a number of variables, such as changes in load, and a wide range of speeds at the leveling zone which, make accurate deceleration and leveling of the car at the selected landing by the main drive circuit unreliable.
The leveling zone is generally defined by a landing and leveling transducer mounted on the car and a vane mounted in the hoistway at each potential landing. The leveling transducer typically includes units carried by the car and a vane mounted in the hoistway at each landing. In some systems, a set of magnetic units carried by the car are operated by a vane in the hoistway. In many systems, a carefully profiled vane is mounted in the hoistway, and a non-contacting sensor is mounted on the elevator car. The sensor may, for example, include a set of electromagnetic or optical units. The vane is shaped to cause the sensor to produce a varying signal as the sensor moves along the vane, and that signal is fed to the elevator motor to bring the elevator to an accurate stop.
The present invention provides an improved elevator landing system.
The landing system of the present invention is particularly well adapted for use in the elevator system shown in Maynard et al., U.S. Pat. No. 3,948,357, assigned to the assignee of the present application. Other typical control circuits, in which the present invention would also be usable, are shown in U.S. Pat. No. 3,777,855 to Boyldew et al., and in U.S. Pat. No. 4,155,426 to Booker, for example.
As shown in U.S. Pat. No. 3,948,357 to Maynard et al, U.S. Pat. No. 3,749,203 to Hoelscher, U.S. Pat. No. 3,983,961 to Aron, U.S. Pat. No. 3,207,265 to Lund et al., and U.S. Pat. No. 4,318,456 to Lowry, prior art landing systems generally operate with a fixed, predetermined profile of velocity against position. The predetermined profile usually changes the car's velocity in proportion to the square root of the distance remains to the landing, so as to provide a constant deceleration. In the last fraction of an inch of the car's travel, the landing system generally utilizes a predetermined terminal crawl speed of above five feet per minute.
As the elevator car approaches a leveling zone, the elevator system's main drive circuit seeks to match the deceleration and speed of the car to the predetermined landing profile, so as to provide a smooth transition to the landing system. Because of the limitations of practical systems, this matching is not always possible, and the transition is not always smooth.
Because of the inflexibility of conventional elevator landing systems, the time required for landing the elevator car is sometimes quite slow, and on short trips the time required for the last twenty or so inches before landing may be a large proportion of the total travel time. This reduces the efficiency of the elevator system.
Because the landing system utilizes a square root function, the transition to the crawl speed is also not smooth.